ceradyne makes ceramic products used in the defense and auto industries. for instance, it makes lightweight armor for military helmets. conglomerate 3-m is the buyer. the price tag is about $860 million, including ceradyne's cash and short term investments. ceradyne shares will get $35 per share. the offer sent shares of ceradyne up 43.1 on heavy volume. the stock closed just shy of the buyout price. the buyer: 3m, moved 0.9% higher, closing about $1 below a 52 week high. just a month ago, 3-m scrapped plans to buy the officer and consumer products division of avery dennison. that deal died after the department of justice threatened to sue over anti-trust concerns. there's no deal for business software firm b.m.c., but it is looking for one. the stock rallied 3.3% today after the wall street journal reported the company has hired bank of america merrill lynch to drum up interest from a potential buyer. meantime, honeywell is making a play in the natural gas business, buying 70% of the privately held thomas russell company, an energy equipment supplier. hon